Changes in the Cell Surface Level of GP126 during Development of Dictyostelium discoideum

Abstract

The developmental regulation of the vegetative cohesion molecule, gp126, has been monitored in the cellular slime mould Dictyostelium discoideum. As judged by immunoprecipitation using an anti-vegetative cell, cohesion blocking antibody, gp126 persisted until at least the grex stage of development although a decline in the level of the molecule was observed thereafter. Further, after the grex stage, cells showed an increasing loss of ability to absorb the cohesion-blocking effect of an anti-vegetative cell Fab. Therefore, the decline of gp126 could be ascribed to a loss from the cell surface. By radio-iodination of vegetative cells followed by liquid-scintillation counting of gp126, developmental-regulation could be determined quantitatively.At the grex stage of development, whole aggregates were embedded in wax. Longitudinal sections were then stained with a monospecific anti-gpl26 Fab, followed by a fluorescent sheep anti-rabbit IgG. Fluorescence was observed only at the tip (the prestalk) region, thereby showing that gp126 is a prestalk marker.To confirm the above result, grexes were dissociated and cells were separated into prespore and prestalk populations on a gradient of Percoll. Prestalk but not prespore cells were able to absorb the cohesion-blocking effect of an anti-vegetative cell Fab.To examine the biosynthesis of gpl26, cells were pulsed with radioactive glucosamine, mannose or acetate. The pattern of incorporation of radioactivity suggested that the de novo synthesis of gp126 ceases upon commencement of development.

Two distinct adhesion systems are responsible for EDTA-sensitive adhesion in Dictyostelium discoideum

“…The timing of gp24 synthesis during development is consistent with this conclusion. gp126 is also synthesized during growth however its synthesis ceases when development is initiated [4]. Therefore the time course of gp126 synthesis suggests that gpl26 does not participate in cs C-mediated adhesion.…”

“…More specific polyclonal antibodies directed against gp126 block adhesion between D. discoideum grown to high density, block the ingestion of Eschevichia coli, and inhibit adhesion to a glass substratum [6]. gp126 is present in growing amoebae and although its synthesis stops when development is initiated, it is present on migrating pseudoplasmodia [4]. Currently there is no evidence which suggests that the adhesion observed when amoebae are grown to high density, that attributed to cs B, is the result of more than one adhesion system.…”

Glycoprotein gp130 ofDictyostelium discoideumInfluences Macropinocytosis and Adhesion

“…Postulated to be a phagocytosis receptor (Chia, 1996), gp130 is possibly the same molecule as gp126, a surface-exposed glycoprotein suggested to have a dual role as both a phagocytosis receptor and a mediator of cell-cell cohesion (Chadwick and Garrod, 1983;Chadwick et al, 1984;Chadwick, 1986). Characteristics of gp130 consistent with a role in phagocytosis are its presence in phagosomes, an association with detergent (Triton X-100)-insoluble cytoskeletons of bacterially grown cells but a depletion from membranes because of its internalization during phagocytosis (Chia, 1996;Rezabek et al, 1997), and the presence of an altered form in a D. discoideum phagocytosis mutant (Vogel et al, 1980).…”